Moisture-proof combustible cartridge case



United States Patent 1111 3,550,532

{72] Inventor Theodore Zimmerman [56] References Cited 66 St. Charles Avenue, West Caldwell, NJ. UNITED STATES PATENTS 1,808,877 6/1931 Young 102/38(X) [2i] P 66359 1.862.914 6/1932 Wagner 149 12 [22] Aug-25,1967 3,236,704 2/1966 Axelrod et a]. 102/43 x I451 Pale-med kc-2911970 3,280,746 10/1966 Brown 102/43 3,304,867 2/1967 Nadel lO2/38(X) 3,139,355 6/1964 De Fries etal..... l02/43(X) 3,320,886 5/1967 De Luca .r 102/43 [541 MOISTURE-PROOF COMBUSTIBLE CARTRIDGE Prim? stall CASE Attorney-Edward Goldberg 19 Claims, 3 Drawing Figs.

[52] U.S. Cl 102/43, ABSTRACT: Combustible cartridge cases of fibrous materials 86/20; 149/12; 102/228; 264/3 are impregnated with an aliphatic nitrated ester, a stabilizer [51] Int. Cl F42b 5/18 and a resin binder to prevent penetration of moisture into the [50] Field of Search lO2/38,43; cartridge case materials and contents while permitting high 264/3; 149/2, 12 ballistic performance.

KRAFT AND OTHER F/EERS AUPHAT/C IWIRATD $7k/0$N$II7Z!R/ SOL VENT "STAG/l/ZER 2a PRfF'ORM MESSURE M/x'R DIES HEAT VACUUM ,g sense/v any WA7'ER l, R'S/N -26 5L O/P TAA/k 15%,?

" me'ssme 015$ SHOT DISPENSER s u RES/N FIN/SHE 3a PRODUCT VA (l/UM TANK C/RC'l/lAT/NG FE TING PUMP TANK 1 MOISTURE-PROOF COMBUSTIBLE CARTRIDGE CASE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a composition and method providing an improved combustible cartridge case and particularly to a solution which is mixed with the materials of the case to eliminate moisture absorption and form a completely waterproof composition.

2. Description of the Prior Art Present combustible cartridge cases are generally made of nitrocellulose and kraft fibers which are dispersed in water and collected onto a felting die. The materials are then molded into a desired shape and impregnated with a polyvinyl fonnal resin. A more detailed description of the process may be found in US. Pat. No. 3,320,886 issued May 23, 1967. This type of cartridge case however, particularly the kraft fibers, when subjected to high humidity and temperature conditions, absorbs moisture which degrades the ballistic performance.

Various attempts to solve this problem have included the use of plastic film coatings on the cartridge case surface or incorporation of water repellent chemicals into the case material. These films were often not completely consumed during the ballistic firing cycle and would leave an unacceptable amount of residue in the gun breech which could interfere with the loading of the next cartridge or smoulder and cause accidental preignition. Incomplete combustion can result in a dangerous flare back upon opening the breech immediately after firing. In addition. moisture penetration affects the physical properties of the materials and lowers the ballistic velocity level. Water repellent agents such as silicone oils also have left a residue in the gun chamber which interfered with electrical continuity of an electrically actuated combustible primer in a gun weapon system such as described in US. Pat. No. 3,249,049.

Existing methods have partially alleviated the problem by packaging the cartridge case in a quickly removable moisture proof bag. This method however is undesirable in combat conditions wherein the bag must be removed just prior to loading the cartridge in the gun.

SUMMARY OF THE INVENTION It is therefore the primary object of the present invention to provide a completely combustible moisture proof composition for a cartridge case which leaves no residue in the gun breech and maintains the required physical properties and ballistic velocity levels for long periods of time under extreme variations of temperature and humidity.

These objects and advantages are achieved by a novel composition and method which includes mixing a solution of a aliphatic nitrated ester, a stabilizer and a resin binder with kraft, sisal or synthetic fibers to form an improved combustible waterproof cartridge case. The invention will be more fully understood by reference to the accompanying drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a typical cartridge case which is made with the composition and method of the present invention;

FIG. 2 is a flow diagram of the steps in the novel process;

and

FIG. 3 is an alternative method for providing the novel composition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS sary to provide physical strength to the cartridge case composition and to control the interior ballistic level without adding extensively to the internal energy of the composition or affecting the burning rate characteristics.

It has now been found that the kraft and other fibers of the composition can be impregnated with a solution of an aliphatic nitrated ester of aliphatic hydroxyl compounds, a suitable stabilizer and a resin binder which prevent penetration of moisture into the combustible cartridge case. The aliphatic nitrated ester should be nearly insoluble in water and have an oily characteristic. Examples of suitable ingredients of this type are nitroglycerin, glycerol monolactate trinitrate, diethylene glycol dinitrate, metriol trinitrate, l, 2, 4 butanetiol trinitrate, diethylene glycol dinitrate, nitroisobutylglycerol trinitrate and triethylene glycol dinitrate.

Manufacture of a typical composition incorporating an aliphatic nitrated ester such as nitroglycerin is described in connection with the flow diagram of FIG. 2 The process may be either a batch or a continuous one. A slurry paste is form ed by mixing kraft and nitrocellulose fibers (l2l3/z percent nitrogen content) with a solution of nitroglycerin and triacetin in a suitable solvent such as ether, acetone, benzene, methanol, toluene or xylene in a ratio of approximately 40 percent nitroglycerin to 10 percent triacetin and the remainder solvent. The triacetin acts as a diluent to desensitize the nitroglycerin. Other substances which may serve this purpose are methanol or ether. The diluent may be reduced or eliminated when used with more stable aliphatic nitrated esters. The solvent, which is relatively volatile, remains in the solution only temporarily as it evaporates during the process. Other fibers such as sisal, cotton linters or wood pulp may also be added, with the solution being absorbed into the fibers to form the paste. A stabilizer such as diphenylamine, 2 nitrodiphenylamine or ethyl or methyl centralite may be incorporated into the paste at this point. This stabilizer prevents deterioration of the nitrated compounds with time, enhances shelf life and may also serve as a desensitizer.

The paste is agitated rapidly and beaten in a mixing tank 12 until it has a fine texture. The fibers are then passed through a fine mesh screen 14 and into a water bath to form a slurry in a tank 16. This operation can be used in the process for blending with other batches to produce uniform materials. A shot dispenser 18 makes up the required concentration of materials for collection on a porous former in a standard felting process, as described in the aforementioned U.S.Pat. No. 3,320,886. This step is carried out in felting tank 20 and provides a shaped body of waterproof material for the cartridge case. The felted preform is then inserted into a first set of preform dies 22 with heat and pressure applied to obtain the desired physical characteristics and vacuum dried 24 to remove excess liquids. The molded case is then dipped in a suitable resin 26 and the excess resin is squeezed out in the final strike dies 28 under heat and pressure to provide the finished product 30 having specified dimensions. The temperature range may be about F. to 300 F. and the pressure applied by air or mechanical means may be from 25 to 400 p.s.i.

The aliphatic nitrated ester, besides providing waterproofing, also acts as a plasticizer and under these conditions the felted material will flow to some extent to facilitate reproduction of the case to the dimensions of the mod. The solubility of nitroglycerin is 0.18 grams per 100 ml. H 0 at 20 C., and as a plasticizer it provides a tougher material which is waterproof and also has the properties of a combustible chemical propellant. The amount of nitroglycerin penetrating the kraft fibers may be directly controlled by the quantity of nitroglycerin to triacetin to solvent solution added to the inert kraft and cellulose fibers. The process thus may be accurately controlled to provide desired burning rate characteristics. The quality of the finished product may be easily monitored by analyzing the composition for the presence of nitrates and/or the aliphatic nitrated ester. The nitrocellulose fibers may be eliminated entirely since a mixture of only inert fibers such as kraft with the aliphatic nitrated ester is sufficient for proper combustion. Ex-

cellent interior and exterior ballistic uniformity is obtainable using granular propellant powder with the present combustible cartridge case as the container.

The following formulations are examples of combustible case materials prepared -in accordance with the method described above. The approximate relative proportions are given by weight on a dry basis without solvent.

Exam le 1 itroglycerin percent- 1 Triacetin do 4 Nitrocellulose (12 %N) do 50 Resin Binder do 17 Kraft do 13 Di henylamine do 1 Exam e 2: I

N itroglycerin -percent- '15 Triacetin do 4 Kraft do 63 Resin Binder do 17 Diphenylamine do 1 Other aliphatic nitrated esters of aliphatic hydroxyl compounds including glycerol monolactate trinitrate, glycol dinitrate, metriol trinitrate, l, 2, 4 butanetiol trinitrate, diethylene glycol dinitrate, nitroisobutylglycerol trinitrate and triethylene glycol dinitrate may be substituted directly for the percentage of nitroglycerin. Thus 15 percent by weight of glycerol monolactate trinitrate may replace the 15 percent nitroglycerin with the other ingredients remaining the same. The 1 percent of diphenylamine stabilizer may be replaced by slightly larger percentages of ethyl or methyl centralite with compensating minor changes in the remaining ingredients which are noncritical. Examples of suitable resin binders that may be used are polyvinyformal and phenol formaldehyde resins. acrylic, acetal, acrylonitrile-butadicne styrene copolymers, cellulose acetate, polyamides and polystyrene.

The proportion of aliphatic nitrated esters may vary in a range between 5 percent to 30 percent, with the other ingredients changing accordingly as below:

Example 3 Glycerol monolactate trinitratm -percent- 5 Nitrocellulose (12 %N) do 64 Polystyrene do- 1 7 Kraft do- 13 Di henylamine do 1 Exam e 4: v

itroglycerin percent- 30 Triacetin do -7 Nitrocellulose (12 %N) do 40 Cellulose Acetate do 15 Kraft do 5 Ethyl centralite do 3 Another method of incorporating nitroglycerin, metriol trinitrate or other aliphatic nitrated esters into kraft and other fibers may be accomplished in the following manner, -as illustrated schematically in FIG. 3.

Mix the kraft fibers with the triacetin diluent in a ratio of 3 to 40 percent by weight of triacetin to kraft at a temperature range between 80 F. to l80 F. The mixing time varies until a uniform paste is obtained. Other immiscible diluents such as benzene. toluene, xylene, or ether may be used. The resultant paste is then mixed with an equal amount of water in a vented tank 32 under rapid agitation by agitator 34. A stabilized nitroglycerin/acetone solution is added to the slurry of kraft, triacetin and water by distributor 36. The nitroglycerin/acetone solution may contain 70 percent nitroglycerin with a small proportion of stabilizer and 30 percent acetone or other solvent which also provides a temporary desensitizing action. The nitroglycerin and solvent will be absorbed by the kraft triacetin mixture, the latter being almost immiscible with water. The solubility of triacetin in water is 7.17 grams per ml. of water. The nitroglycerin is soluble in triacetin in all proportions and will be absorbed by the kraft triacetin and remain desensitized. The kraft, triacetin and nitroglycerin mixture can then be directly added through a shot dispenser to the felting tank. The flow of material will then follow the normal felting and molding process as previously described in connection with FIG. 2.

A third method of incorporating an aliphatic nitrated ester with kraft fibers can be accomplished by a simple dip coating process. A previously formed cartridge case of nitrocellulose, kraft and other optional fibers such as sisal, with a resin binder and stabilizer included therein, can be dipped into a solution, for example, of about 10 percent nitroglycerin or other aliphatic nitrated ester, 2 percent 2 nitrodiphenylamine and 88 percent solvent. The solvent may be ether, benzene or any of those mentioned above. The inert kraft and sisal fibers will absorb the nitroglycerin. Any excess nitroglycerin and solvent is then removed in a set of squeeze dies and the cartridge case vacuum dried in an oven at 100 F. to F. for a suitable period of time, such as about 3 hours.

In a further variation of the process, the kraft and other fibers may be mixed directly with water to form a paste in tank 12 of FIG. 2 and then a slurry, with the aliphatic nitrated ester and other elements in the solution being omitted at first. The felting, preform molding and drying operations are performed as previously. The aliphatic nitrated ester, desensitizer, stabilizer and solvent, as shown by the dash line 38 are then combined with the resin dip 26, in suitable concentration and the molded case dipped into the solution for a suitable period of time, The excess solution is then squeezed out under heat and pressure and the final dimensions established in the final molding step 28.

It may thus be seen that the present invention provides a novel simplified method and composition for a combustible waterproof cartridge case of high ballistic performance.

Iclaim:

1. A waterproof combustible cartridge case composition comprising a molded cartridge case body of felted combustible fibers including kraft fibers, said body being impregnated with an aliphatic nitrated ester, a stabilizer for said aliphatic nitrated ester and a resin binder.

2. The combustible cartridge case composition of claim 1 wherein said aliphatic nitrated ester is of the group consisting of nitroglycerin, glycerol monolactate trinitrate, glycol dinitrate, metriol trinitrate, 1, 2, 4 butanetiol trinitrate, diethylene glycol dinitrate, nitroisobutylglycerol trinitrate and triethylene glycol.

3. The combustible cartridge case composition of claim 2 wherein said aliphatic nitrated ester comprises from between 5 percent to 30 percent of the dry weight of said body.

4. The combustible cartridge case composition of claim 2 including a desensitizer for said aliphatic nitrated ester wherein said desensitizer is of the group consisting of triacetin, methanol and ether.

5. The combustible cartridge case composition of claim 2 wherein said body includes nitrocellulose fibers.

6. The combustible cartridge case composition of claim 3 wherein said stabilizer is of the group consisting of diphenylamine, 2 nitrodiphenylamine, ethyl centralite and methyl centralite.

7. The combustible cartridge case composition of claim 4 wherein said aliphatic nitrated ester is nitroglycerin and said desensitizer is triacetin.

8. A method for making a waterproof combustible cartridge case comprising forming a composition of felted combustible fibers including kraft fibers, impregnating said composition with a solution including a solvent, an aliphatic nitrated ester and a stabilizer for said aliphatic nitrated ester, and molding and drying said composition to a predetermined shape.

9. The method of claim 8 including mixing and impregnating kraft fibers with said solution including a desensitizer for said aliphatic nitrated ester. forming said impregnated fibers into a molded body, drying said body, impregnating said body with a resin binder and reforming and drying said body to the final dimensions.

10. The method of claim 8 comprising forming a body of molded nitrocellulose and kraft fibers, including said stabilizer and a resin binder, impregnating said body with a solution including said solvent and said aliphatic nitrated ester and drying said body.

11. The method of claim 8 wherein said aliphatic nitrated ester is of the group consisting of' nitroglycerin. glycerol monolactate trinitrate, glycol dinitrate, metriol trinitrate, 1, 2, 4 butanetiol trinitrate, diethylene glycol dinitrate, nitroisobutylglycerol trinitrate and triethylene. glycol.

12. The method of claim 8 wherein said composition includes nitrocellulose fibers. I

13. The method of claim 8 wherein-said stabilizer is of the group consisting of diphenylamine, 2 nitrodiphenylamine, ethyl centralite and methyl ce ntralite.

14. The method of claim 8 wherein said solvent is of the group consisting of ether, acetone, benzene, methanol, toluene and xylene.

15. The method of claim 8 including mixing said fibers with water to form a slurry, felting fibers from said slurry to form a body having a predetermined shape. molding and drying said body to provide predetermined characteristics, impregnating said body with said solution including a desensitizer for said aliphatic nitrated ester and a resin binder, and remolding and drying said body to the final dimensions.

16. The method of claim 9 wherein said desensitizer is of the group consisting of triacetin, methanol and ether.

17. The method of claim 9 wherein said aliphatic nitrated ester is nitroglycerin and said desensitizer is triacetin,

18. The method of claim 9 including mixing said fibers in said solution to form a fine paste, immersing said paste in water to form a slurry, felting fibers from said slurry to form a body having a predetermined shape, molding and drying said body to provide predetermined characteristics, impregnating said body with a resin binder and remolding and drying said body to the final dimensions.

19. The method of claim 18 wherein said slurry is formed by first mixing said fibers with a desensitizer relatively immiscible with water to form a paste, mixing the paste with water and adding a solution including said solvent, said aliphatic nitrated ester and said stabilizer. 

